In internal combustion engines of this kind, the exhaust plant usually includes merely a silencer which is arranged externally of the shroud, because disposition of the same within the shroud would make the supervision and servicing very difficult, which in turn could make for serious damage. The tightening of the noise of the exhaust silencer which is disposed externally of the shroud and secured to the engine block is usually performed by wrapping this silencer in sound-deadening layers of suitable material, for example rock wool, which moreover may be held together by a jacket of sheet metal which completely surrounds the silencer. It has been found, however, that as a result of heavy vibrations of the silencer and the metal jacket, which can be induced from the engine block during operation of the engine, the aforesaid interposed layers can be badly damaged in places where, for example, there is a direct engagement, that is to say material contact, between the silencer and its metal jacket. These areas then transmit the vibration to the exterior, wherefore in this construction the noise abatement at the exhaust silencer is considerably reduced, and may even be completely negatived.
Now it is an object of the present invention to avoid this drawback of the known exhaust silencing system and provide a secure, efficient but nevertheless economical type of silencing system.
This object is met in the present invention by the fact that the combustion gases are conducted through an exhaust plant of known form arranged externally of the shroud and connected to the engine block, and that a separate enclosure is provided and secured to the shroud, this enclosing the exhaust plant leaving the small air gap on all sides between the plant and the enclosure with only the exhaust pipe of the plant projecting from the enclosure through an opening. In this way, there is an air layer between the exhaust elements and the enclosure on all sides which prevents direct transmission to the enclosure of vibrations from the exhaust elements which are mounted on the engine block, this having a very powerful noise deadening effect. In addition, this cushion of air inhibits the vibrations of the outer walls of the elements, which can be produced by heavy pressure fluctuations in the exhaust gases (wall pulsations), to be transmitted to the enclosure. These pulsations are also prevented from becoming manifest as damaging air. The enclosure is carried entirely by the shroud and has no contact with the exhaust elements or the engine block. The shroud itself is in turn connected to the engine block with the interposition of anti-vibration means. In this way, the enclosure is adequately screened against undesirable transmission of vibrations from the engine block. In accordance with another feature of the invention, the enclosure is made of sheet metal. By this means, the accepted recognition of the fact that a sheet metal wall alone acts as a very good noise-dampening means is utilized in the present case to increase the deadening effect.
Moreover, sheet metal as a material for the enclosure confers advantages in the production. In the case of exhaust plants with silencers of the known elongated form, in accordance with an embodiment of the invention, the enclosure comprises a jacket which encloses the silencer from the sides and is connected to the shroud, and two covers connected to the jacket, one of these covers having an opening for the passage of the exhaust pipe from the silencer. To avoid contact between the silencer and the enclosure in the event of vibration of the latter, this silencer is secured to the exhaust manifold secured firmly to the engine block and additionally to a support element firmly anchored to the engine block.
The arrangement of the exhaust silencer and the enclosure can be suited to local requirements at any suitable part of the engine. In the case of internal combustion engines with a cooling air fan which conducts air into the spaces between the block and the shroud, it is, however, particularly advantageous to adopt an arrangement in which the enclosure with the silencer is disposed in the vicinity of the exit of the cooling air from the shroud. No heat sealing elements need be introduced at the parts where the enclosure is attached because there is a heat transfer from the enclosure to the air discharge from the shroud and it is, therefore, not detrimental.
A simple automatic heat dispersion from the interior of the enclosure can in addition be achieved in an arrangement with an elongated and substantially vertically-disposed exhauster silencer in a further feature of the invention, in which the enclosure has a free opening, approximately at its uppermost part to vent heated air upwardly from the interior of the enclosure under a thermal effect. In accordance with yet another feature of the invention, a particularly simple constructional arrangement is acquired where a vertically-extending gap is left open between the longitudinal edges of the jacket at the fastened side of the latter to provide a flue for the entry and exit of air.
In order, further, to reduce the muzzle noise of the exhaust silencer, in accordance with a further feature of the invention, use is made of a muzzle silencer which is secured to the cover concentrically with the passage opening in the latter and freely surrounds the exhaust pipe of the latter.
To conduct the combustion gases to a suitable part of the surroundings, in accordance with a further feature of the invention, a rigid or flexible extension pipe is secured to the cover concentrically with the opening in the latter, and the exhaust pipe of the silencer opens into this to provide a simple discharge for waste gas at the required point.